Fluorine-18 labeled rhodamine derivatives for imaging with positron emission tomography

ABSTRACT

The present invention is directed toward novel fluorine-18 labeled rhodamine dye derivatives and methods of making the same. The present invention is also directed toward methods of using novel fluorine-18 labeled rhodamine dye derivatives as positron emission tomography imaging agents and myocardial perfusion imaging agents.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation application of co-pending U.S. patentapplication Ser. No. 12/479,520 filed Jun. 5, 2009 which is aContinuation-in-Part of International PCT Application No.PCT/US2008/065300, filed May 30, 2008, which claims the benefit under 35U.S.C. §119(e) to U.S. Provisional Application Ser. No. 60/932,308,filed May 30, 2007, the contents of each of which are incorporatedherein by reference in their entireties.

FIELD OF THE INVENTION

The present disclosure relates to ¹⁸F-labeled dye compounds, methods ofmaking the same, and their use for positron emission tomography imaging,particularly myocardial perfusion imaging, of a subject.

BACKGROUND OF THE INVENTION

Myocardial perfusion imaging (MPI) is a diagnostic technique useful forthe detection and characterization of coronary artery disease. Perfusionimaging uses materials such as radioisotopes to identify areas ofinsufficient blood flow.

Radioisotopes are commonly used in contemporary medical imaging. One ofthe most important clinically-employed radioisotopes is technetium-99m(^(99m)Tc). Other radioisotopes, including halogens, such as ¹⁸F, ¹²⁵I,¹³¹I and ⁸²Br, and isotopes of various metal radionuclides of lead,gallium, rhenium, rubidium, arsenic and copper, have also been exploredas potential imaging agents. Medical imaging is used in a variety ofmedical applications, including imaging of the brain, tumors, andcomponents of the cardiovascular system.

Perfusion agents are currently one of the most important tools fordetermining heart function. Tl-201, Tc-99-MIBI and Tc-99-tetrofosmin arein routine use for myocardial imaging at rest and after exercise. Theseagents are very useful but are not optimal. These tracers aresingle-photon imaging agents and the utility is limited by theproperties of existing single-photon emission computed tomography(SPECT) imaging cameras and technology. Positron Emission Tomography(PET), however, has several advantages in comparison to SPECT includinghigher image resolution and more straightforward attenuation correction.Fluorine-18 is a positron-emitting radionuclide whose physicalproperties (t_(1/2)=110 min., 97% positron yield) are well suited to PETimaging, and the number of PET cameras and imaging centers are growingrapidly in response to the increased availability of ¹⁸F, particularlyas [¹⁸F]FDG (2-fluorodeoxyglucose).

Fluorine-18 is one of the most useful positron emitting radionuclidescurrently being used in clinical nuclear medicine diagnosis. Forexample, 2-[¹⁸F]FDG (2-[¹⁸F]-fluoro-2-deoxy-D-glucose) is theradiopharmaceutical of choice for the diagnosis of several cancers andbrain disorders. This radiopharmaceutical produces superiorhigh-resolution images and quantitative data about regional uptake bytissue. The 110-min half-life of ¹⁸F allows production and distributionof 2-[¹⁸F]FDG to nuclear medicine facilities that do not have access toa cyclotron. The relatively long physical half-life of ¹⁸F also permitsPET studies of moderately slow physiological process. Decay of ¹⁸F islargely by positron emission (97%), and the emitted positron is ofrelatively low energy (maximum 0.635 MeV) and thus has a short meanrange (2.39 mm in water). Fluorine-18 is readily available from bothparticle accelerators and nuclear reactors using a wide variety ofnuclear reactions, and can be produced at specific activitiesapproaching the theoretical limit of 1.171×10⁹ Ci/mmol.

Myocardial perfusion imaging (MPI) is extremely useful in the diagnosisof cardiac disease. PET (positron-emission tomography) MPI providesfunctional images of high quality that can be co-registered with[¹⁸F]FDG images to delineate regions of infarct and ischemia.Short-lived compounds such as [¹⁵O]H₂O, [¹³N]NH₃, and ⁸²Rb are wellestablished PET MPI tracers, but PET centers without a cyclotron arelimited to using ⁸²Rb, which has significant limitations including highcost and high positron energy.

The present invention is directed to overcoming these and otherdeficiencies in the art.

SUMMARY OF THE INVENTION

According to one aspect of the invention there are provided novelfluorine-18 labeled rhodamine derivatives which are represented byformulas I and II:

wherein R₁₀, R₁₁, R₁₂, R₁₃ and R₁₄ are each independently selected fromthe group consisting of hydrogen, substituted or unsubstituted alkyl,substituted or unsubstituted alkenyl, substituted or unsubstitutedalkynyl, substituted or unsubstituted heterocycloalkyl, substituted orunsubstituted alkoxy, substituted or unsubstituted carbonyl, acylamino,halogen, halogen radioisotope, substituted or unsubstituted aryl,substituted or unsubstituted heteroaryl, substituted or unsubstitutedamino, substituted or unsubstituted alkylamino, substituted orunsubstituted arylamino and isothiocyano;

wherein R₂ and R₃, taken together with the nitrogen atom to which theyare attached, may optionally form a substituted or unsubstitutedheterocyclic ring system;

R₂ and R₁₀, taken together with the atoms to which they are attached,may optionally form a 5- or 6-membered heterocyclic ring;

R₂ and R₁, taken together with the atoms to which they are attached, mayoptionally form a 5- or 6-membered heterocyclic ring; and

R₃ and R₄, taken together with the atoms to which they are attached, mayoptionally form a 5- or 6-membered heterocyclic ring or a substituted orunsubstituted heterocyclic ring system;

A₁ is carbon or nitrogen, if A₁ is nitrogen, then R₆ is absent;

R₆ is absent or selected from the group consisting of hydrogen,substituted or unsubstituted alkyl, substituted or unsubstitutedalkenyl, substituted or unsubstituted alkynyl, substituted orunsubstituted heterocycloalkyl, substituted or unsubstituted alkoxy,substituted or unsubstituted carbonyl, acylamino, halogen, halogenradioisotope, substituted or unsubstituted aryl, substituted orunsubstituted heteroaryl, substituted or unsubstituted amino,substituted or unsubstituted alkylamino, substituted or unsubstitutedarylamino, isothiocyano;

R₇, R₈ and R₉ are each independently selected from the group consistingof hydrogen, substituted or unsubstituted alkyl, substituted orunsubstituted alkenyl, substituted or unsubstituted alkynyl, substitutedor unsubstituted heterocycloalkyl, substituted or unsubstituted alkoxy,substituted or unsubstituted carbonyl, acylamino, halogen, halogenradioisotope, substituted or unsubstituted aryl, substituted orunsubstituted heteroaryl, substituted or unsubstituted amino,substituted or unsubstituted alkylamino, substituted or unsubstitutedarylamino, isothiocyano;

R₁₅ is independently selected from the group consisting of ¹⁸F-labeledsubstituted or unsubstituted alkyl, ¹⁸F-labeled substituted orunsubstituted alkenyl, ¹⁸F-labeled substituted or unsubstituted alkynyl,¹⁸F-labeled substituted or unsubstituted heterocycloalkyl, ¹⁸F-labeledsubstituted or unsubstituted alkoxy, ¹⁸F-labeled substituted orunsubstituted carbonyl, ¹⁸F-labeled acylamino, halogen radioisotope,¹⁸F-labeled substituted or unsubstituted aryl, ¹⁸F-labeled substitutedor unsubstituted heteroaryl, ¹⁸F-labeled substituted or unsubstitutedamino, ¹⁸F-labeled substituted or unsubstituted alkylamino, ¹⁸F-labeledsubstituted or unsubstituted arylamino, ¹⁸F-labeled isothiocyano, and—(CH₂CH₂O)_(m)CH₂CH₂ ¹⁸F, wherein m is 1-50;

R₁₆ is independently selected from the group consisting of hydrogen,substituted or unsubstituted alkyl, substituted or unsubstitutedalkenyl, substituted or unsubstituted alkynyl, substituted orunsubstituted heterocycloalkyl, substituted or unsubstituted alkoxy,substituted or unsubstituted carbonyl, acylamino, halogen, halogenradioisotope, substituted or unsubstituted aryl, substituted orunsubstituted heteroaryl, substituted or unsubstituted amino,substituted or unsubstituted alkylamino, substituted or unsubstitutedarylamino, isothiocyano; and

A- is an anion.

In one embodiment, R₁₅ is ¹⁸F-labeled substituted or unsubstitutedalkyl.

In one embodiment, R₁₅ is —(CH₂)_(n)CH₂ ¹⁸F, wherein n is 1-5.

In one embodiment, R₁₅ is —CH₂CH₂CH₂ ¹⁸F.

In one embodiment, R₁₅ is —(CH₂CH₂O)_(m)CH₂CH₂ ¹⁸F, wherein m is 1-4.

In one embodiment, R₁₅ is —CH₂CH₂OCH₂CH₂ ¹⁸F.

In one embodiment, R₂ and R₃ are alkyl; R₁, R₄, R₅, R₆, R₇, R₈, and R₉are hydrogen; and A₁ is carbon.

In one embodiment, R₂ and R₄ are alkyl; R₁, R₃, R₅, R₆, R₇, R₈, and R₉are hydrogen; and A₁ is carbon.

In one embodiment, R₂ is ethyl.

In one embodiment, R₃ is ethyl.

In one embodiment, R₄ is methyl.

In one embodiment, R₁, R₂, R₃, R₄, R₅, R₆, R₇, R₈, and R₉ are hydrogen;and A₁ is carbon.

In one embodiment, R₃ and R₄, taken together with the atoms to whichthey are attached, form a 6-membered heterocyclic ring and R₂ and R₁,taken together with the atoms to which they are attached, form a6-membered heterocyclic ring.

In one embodiment, R₄ is methyl; and R₂ and R₃ are each independentlyhydrogen or alkyl.

In another aspect, the invention provides a method of imaging myocardialperfusion comprising: administering to a patient a compound of claims1-16; and scanning the patient using diagnostic imaging.

Another aspect of the present invention is directed toward a compositionincluding a fluorine-18 labeled rhodamine derivative according toformula I or II and a pharmaceutically acceptable carrier.

Another aspect of the present invention is directed toward a method ofobtaining a positron emission image of a portion of a mammal includingadministering to a mammal a fluorine-18 labeled rhodamine derivativeaccording to formula I or II and acquiring a positron emission image ofa portion of a mammal.

In one embodiment, the mammal is a human.

In one embodiment, the portion of a mammal is the myocardium.

A further aspect of the present invention is directed toward a method ofimaging myocardial perfusion including administering to a patient afluorine-18 labeled rhodamine derivative according to formula I or IIand scanning the patient using diagnostic imaging.

A further aspect of the present invention is directed toward use of afluorine-18 labeled rhodamine derivative according to formula I or IIfor the production of an imaging agent for carrying out myocardialperfusion imaging.

A still further aspect of the present invention is directed toward useof a fluorine-18 labeled rhodamine derivative according to formula I orII in the manufacture of an imaging agent for carrying outpositron-emission tomography.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a reaction scheme illustrating the synthesis of2-fluoroethyltosylate precursor.

FIG. 2 is a reaction scheme illustrating reaction of2-fluorethyltosylate with rhodamine lactone to form 2-fluoroethylesterof rhodamine B.

FIG. 3 is a reaction scheme illustrating the reaction performed by atwo-step reaction in a single vessel, without isolation of the2-fluoroethyltosylate precursor.

FIG. 4 is a reaction scheme illustrating the synthesis of2-F-fluoroethyl ester of rhodamine 110 as cold reference compound foresters.

FIG. 5 is a reaction scheme illustrating the preparation ofprecursor-2-¹⁸F-fluorethylamine and 2-¹⁸F-fluoroethyl amide of rhodamine110.

FIG. 6 is a reaction scheme illustrating the direct labeling of2-¹⁸F-fluoroethyl amide of rhodamine 110.

FIG. 7 shows of the ¹⁸F-labeled rhodamine B esters.

DETAILED DESCRIPTION OF THE INVENTION

Phenyl xanthene dyes, including rhodamine and rhodol dyes, are known. Itis also known that certain dyes accumulate in mitochondria of livingcells. Fluorine-18 radiolabeling of these dyes is not trivial due to theneed for a suitable precursor and the appropriate conditions forradiolabeling. Here we describe such radiolabeled dyes and methods oftheir use as Positron Emission Tomography imaging agents.

The phenyl xanthene dyes comprise any fluorescein, rhodol or rhodaminering system where the phenyl substituent at the 9-carbon (“the C9 phenylring”) is a specific type of phenyl ring. For the purposes of thisdescription, fluoresceins, rhodols and rhodamines are numbered in thefollowing manner in formula (III):

where A is either a hydroxyl or an amine group and B is a either an oxoor an imminium group. The C9 phenyl ring on the phenyl xanthene dye,whether substituted or unsubstituted, may be referred to as the “lowerring.” The remainder of the molecule may be referred to as the “upperring system.”

The C9 phenyl ring is substituted at one or both of carbons C11 or C15with a group selected from substituted or unsubstituted alkyl,heteroalkyl, alkoxy, halo, haloalkyl, amino, amido, alkylthio,carboxylic acid, ester, ether, cyano, isocyano, cyanato,mercaptocyanato, nitro, and sulfinyl. When both the C11 and C15 carbonsare substituted, the substituents may be the same or different.

Any dye having this type of configuration is suitable. Preferredembodiments include rhodamine dyes wherein the C9 phenyl ring issubstituted with a —COOH group. Preferred location for the —COOHsubstitution are C11 or C15. Examples of such rhodamine dyes are, butnot limited to, rhodamine 590, rhodamine 110, rhodamine 101, rhodamine575, and, preferably rhodamine 610. Further substitutions, such asnucleophilic substitution, may be made at any position as long as thereremains room for an ¹⁸F.

Fluorine-18 is a positron-emitting radionuclide whose physicalproperties (t_(1/2)=110 min., 97% positron yield) are well suited to PETimaging, and the number of PET cameras and imaging centers are growingrapidly in response to the increased availability of ¹⁸F, particularlyas [¹⁸F]FDG (2-fluordeoxyglucose).

Fluorine-18 is one of the most useful positron emitting radionuclidescurrently being used in clinical nuclear medicine diagnosis. Forexample, 2-[¹⁸F]FDG (2-[¹⁸F]-fluoro-2-deoxy-D-glucose) is theradiopharmaceutical of choice for the diagnosis of several cancers andbrain disorders. This radiopharmaceutical produces superiorhigh-resolution images and quantitative data about regional uptake bytissue. The 110-min half-life of ¹⁸F allows production and distributionof 2-[¹⁸F]FDG to nuclear medicine facilities that do not have access toa cyclotron. The relatively long physical half-life of ¹⁸F also permitsPET studies of moderately slow physiological process. Decay of ¹⁸F islargely by positron emission (97%), and the emitted positron is ofrelatively low energy (maximum 0.635 MeV) and thus has a short meanrange (2.39 mm in water). Fluorine-18 is readily available from bothparticle accelerators and nuclear reactors using a wide variety ofnuclear reactions, and can be produced at specific activitiesapproaching the theoretical limit of 1.171×10⁹ Ci/mmol.

According to one aspect of the invention there are provided novelfluorine-18 labeled rhodamine derivatives which are represented byformulas I and II

wherein R₁, R₂, R₃, R₄, and R₅, are each independently selected from thegroup consisting of hydrogen, substituted or unsubstituted alkyl,preferably having from 1 to 18 carbon atoms, substituted orunsubstituted alkenyl, preferably having from 2 to 18 carbon atoms,substituted or unsubstituted alkynyl, preferably having from 2 to 18carbon atoms, substituted or unsubstituted heterocycloalkyl, substitutedor unsubstituted alkoxy, substituted or unsubstituted carbonyl,acylamino, halogen, halogen radioisotope, substituted or unsubstitutedaryl, substituted or unsubstituted heteroaryl, substituted orunsubstituted amino, substituted or unsubstituted alkylamino,substituted or unsubstituted arylamino, isothiocyano and a compound offormula III

In formula III, R₁₀, R₁₁, R₁₂, R₁₃ and R₁₄ are each independentlyselected from the group consisting of hydrogen, substituted orunsubstituted alkyl, preferably having from 1 to 18 carbon atoms,substituted or unsubstituted alkenyl, preferably having from 2 to 18carbon atoms, substituted or unsubstituted alkynyl, preferably havingfrom 2 to 18 carbon atoms, substituted or unsubstitutedheterocycloalkyl, substituted or unsubstituted alkoxy, substituted orunsubstituted carbonyl, acylamino, halogen, halogen radioisotope,substituted or unsubstituted aryl, substituted or unsubstitutedheteroaryl, substituted or unsubstituted amino, substituted orunsubstituted alkylamino, substituted or unsubstituted arylamino andisothiocyano; IP In formulas I and II, R₂ and R₃, taken together withthe nitrogen atom to which they are attached, can form a substituted orunsubstituted heterocyclic ring system, such as, for example,substituted and unsubstituted morpholines, pyrrolidines, andpiperidines;

R₂ and R₁₀, taken together with the atoms to which they are attached canform a 5- or 6-membered heterocyclic ring such as, for example, indolineor tetrahydroquinoline;

R₂ and R₁ taken together with the atoms to which they are attached, canform a substituted or unsubstituted heterocyclic ring system, such as,for example, substituted and unsubstituted morpholines, pyrrolidines,and piperidines; or

R₃ and R₄, taken together with the atoms to which they are attached, canform a substituted or unsubstituted heterocyclic ring system, such as,for example, substituted and unsubstituted morpholines, pyrrolidines,and piperidines, or a 5- or 6-membered heterocyclic ring such as, forexample, indoline or tetrahydroquinoline.

A₁ is carbon or nitrogen, if A₁ is nitrogen, then R₆ is absent;

R₆ is absent or selected from the group consisting of hydrogen,substituted or unsubstituted alkyl, preferably having from 1 to 18carbon atoms, substituted or unsubstituted alkenyl, preferably havingfrom 2 to 18 carbon atoms, substituted or unsubstituted alkynyl,preferably having from 2 to 18 carbon atoms, substituted orunsubstituted heterocycloalkyl, substituted or unsubstituted alkoxy,substituted or unsubstituted carbonyl, acylamino, halogen, halogenradioisotope, substituted or unsubstituted aryl, substituted orunsubstituted heteroaryl, substituted or unsubstituted amino,substituted or unsubstituted alkylamino, substituted or unsubstitutedarylamino and isothiocyano;

R₇, R₈ and R₉ are each independently selected from the group consistingof hydrogen, substituted or unsubstituted alkyl, preferably having from1 to 18 carbon atoms, substituted or unsubstituted alkenyl, preferablyhaving from 2 to 18 carbon atoms, substituted or unsubstituted alkynyl,preferably having from 2 to 18 carbon atoms, substituted orunsubstituted heterocycloalkyl, substituted or unsubstituted alkoxy,substituted or unsubstituted carbonyl, acylamino, halogen, halogenradioisotope, substituted or unsubstituted aryl, substituted orunsubstituted heteroaryl, substituted or unsubstituted amino,substituted or unsubstituted alkylamino, substituted or unsubstitutedarylamino and isothiocyano;

R₁₅ is independently selected from the group consisting of hydrogen,substituted or unsubstituted alkyl, preferably having from 1 to 18carbon atoms, substituted or unsubstituted alkenyl, preferably havingfrom 2 to 18 carbon atoms, substituted or unsubstituted alkynyl,preferably having from 2 to 18 carbon atoms, substituted orunsubstituted heterocycloalkyl, substituted or unsubstituted alkoxy,substituted or unsubstituted carbonyl, acylamino, halogen, halogenradioisotope, substituted or unsubstituted aryl, substituted orunsubstituted heteroaryl, substituted or unsubstituted amino,substituted or unsubstituted alkylamino, substituted or unsubstitutedarylamino and isothiocyano;

R₁₆ is independently selected from the group consisting of hydrogen,substituted or unsubstituted alkyl, preferably having from 1 to 18carbon atoms, substituted or unsubstituted alkenyl, preferably havingfrom 2 to 18 carbon atoms, substituted or unsubstituted alkynyl,preferably having from 2 to 18 carbon atoms, substituted orunsubstituted heterocycloalkyl, substituted or unsubstituted alkoxy,substituted or unsubstituted carbonyl, acylamino, halogen, halogenradioisotope, substituted or unsubstituted aryl, substituted orunsubstituted heteroaryl, substituted or unsubstituted amino,substituted or unsubstituted alkylamino, substituted or unsubstitutedarylamino and isothiocyano;

A- is an anion; and at least one of the R₁-R₁₆ substituents is labeledwith ¹⁸F.

A- is any anion known in the art, such as arsenide, azide, bromide,chloride, fluoride, hydride, iodine, nitride, oxide, phosphide, sulfide,or peroxide, may be used as the anion.

In one embodiment, the invention provides a compound comprising an ¹⁸Flabeled rhodamine derivative according to formula I or II:

wherein R₁, R₂, R₃, R₄, and R₅ are each independently selected from thegroup consisting of hydrogen, alkyl, substituted alkyl, alkenyl,substituted alkenyl, heterocycloalkyl, substituted heterocycloalkyl,alkoxy, substituted alkoxy, substituted carbonyl, acylamino, halogen,and a compound of formula III

wherein R₁₀, R₁₁, R₁₂, R₁₃ and R₁₄ are each independently selected fromthe group consisting of hydrogen, alkyl, substituted alkyl, alkenyl,substituted alkenyl, heterocycloalkyl, substituted heterocycloalkyl,alkoxy, substituted alkoxy, substituted carbonyl, halogen, aryl,substituted aryl, heteroaryl, substituted heteroaryl, amino, substitutedamino, alkylamino, substituted alkylamino, arylamino and substitutedarylamino;

wherein R₂ and R₃, taken together with the nitrogen atom to which theyare attached, may optionally form a substituted or unsubstitutedheterocyclic ring system;

R₂ and R₁₀, taken together with the atoms to which they are attached,may optionally form a 5- or 6-membered heterocyclic ring;

R₂ and R₁, taken together with the atoms to which they are attached, mayoptionally form a 5- or 6-membered heterocyclic ring; and

R₃ and R₄, taken together with the atoms to which they are attached, mayoptionally form a 5- or 6-membered heterocyclic ring or a substituted orunsubstituted heterocyclic ring system;

A₁ is carbon or nitrogen;

R₆ is absent or selected from the group consisting of hydrogen, alkyl,substituted alkyl, alkenyl, substituted alkenyl, heterocycloalkyl,substituted heterocycloalkyl, alkoxy, substituted alkoxy, substitutedcarbonyl, halogen, aryl, substituted aryl, heteroaryl, substitutedheteroaryl, amino, substituted amino, alkylamino, substitutedalkylamino, arylamino, substituted arylamino, and isothiocyano;

R₇, R₈ and R₉ are each independently selected from the group consistingof hydrogen, alkyl, substituted alkyl, alkenyl, substituted alkenyl,heterocycloalkyl, substituted heterocycloalkyl, alkoxy, substitutedalkoxy, substituted carbonyl, halogen, aryl, substituted aryl,heteroaryl, substituted heteroaryl, amino, substituted amino,alkylamino, substituted alkylamino, arylamino, substituted arylamino,and isothiocyano;

R₁₅ is independently selected from the group consisting of hydrogen,alkyl, substituted alkyl, alkenyl, substituted alkenyl,heterocycloalkyl, substituted heterocycloalkyl, alkoxy, substitutedalkoxy, aryl, substituted aryl, heteroaryl, substituted heteroaryl,amino, substituted amino, alkylamino, substituted alkylamino, arylamino,and substituted arylamino;

R₁₆ is independently selected from the group consisting of hydrogen,alkyl, substituted alkyl, alkenyl, substituted alkenyl,heterocycloalkyl, substituted heterocycloalkyl, alkoxy, substitutedalkoxy, aryl, substituted aryl, heteroaryl, substituted heteroaryl,amino, substituted amino, alkylamino, substituted alkylamino, arylamino,and substituted arylamino; A- is an anion; and wherein at least one ofthe R₁-R₁₆ substituents is labeled with ¹⁸F.

In certain embodiments, the ¹⁸F is present on the R₁₅ substituent.

In certain embodiments, when both R₁₅ and R₁₆ are present, the ¹⁸F ispresent on both the R₁₅ and R₁₆ substituent.

In certain embodiments, the R₁₅ substituent is labeled with ¹⁸F and atleast one of the R₁-R₁₄ substituents is labeled with ¹⁸F.

In certain embodiment, when both R₁₅ and R₁₆ are present, both the R₁₅and R₁₆ are labeled with ¹⁸F and at least one of the R₁-R₁₄ substituentsis labeled with ¹⁸F.

In certain embodiments, R₂ and R₃ are alkyl; R₁, R₄, R₅, R₆, R₇, R₈, andR₉ are hydrogen; and A₁ is carbon. In certain embodiments, R₂ is ethyland/or R₃ is ethyl.

In other embodiments, R₂ and R₄ are alkyl; R₁, R₃, R₅, R₆, R₇, R₈, andR₉ are hydrogen; and A₁ is carbon. In certain embodiments, R₂ is ethyland/or R₄ is methyl.

In yet other embodiments, R₁, R₂, R₃, R₄, R₅, R₆, R₇, R₈, and R₉ arehydrogen; and A₁ is carbon.

In certain embodiments, R₃ and R₄ taken together with the atoms to whichthey are attached form a 6-membered heterocyclic ring and R₂ and R₁taken together with the atoms to which they are attached form a6-membered heterocyclic ring.

In other embodiments, R₄ is methyl; and R₂ and R₃ are each independentlyhydrogen or alkyl.

In one embodiment, R₁₅ is independently selected from the groupconsisting of ¹⁸F, ¹⁸F-labeled substituted or unsubstituted alkyl,preferably having from 1 to 18 carbon atoms, ¹⁸F-labeled substituted orunsubstituted alkenyl, preferably having from 2 to 18 carbon atoms,¹⁸F-labeled substituted or unsubstituted alkynyl, preferably having from2 to 18 carbon atoms, ¹⁸F-labeled substituted or unsubstitutedheterocycloalkyl, ¹⁸F-labeled substituted or unsubstituted alkoxy,¹⁸F-labeled substituted or unsubstituted carbonyl, ¹⁸F-labeledacylamino, halogen radioisotope, ¹⁸F-labeled substituted orunsubstituted aryl, ¹⁸F-labeled substituted or unsubstituted heteroaryl,¹⁸F-labeled substituted or unsubstituted amino, ¹⁸F-labeled substitutedor unsubstituted alkylamino, ¹⁸F-labeled substituted or unsubstitutedarylamino, ¹⁸F-labeled isothiocyano and —(CH₂CH₂O)_(m)CH₂CH₂ ¹⁸F,wherein m is 1-50.

In one embodiment, in the ¹⁸F-labeled alkyl, ^(18F)-labeled alkenyl,¹⁸F-labeled alkynyl or ¹⁸F-labeled aryl at least one carbon has beenreplaced by a heteroatom.

In one embodiment, R₁₅ is ¹⁸F-labeled substituted or unsubstitutedalkyl.

In one embodiment, R₁₅ is —(CH₂)_(n)CH₂ ¹⁸F, wherein n is 0-17,preferably n is 1-10, more preferably n is 1-5.

In one embodiment, R₁₅ is —CH₂ ¹⁸F.

In one embodiment, R₁₅ is —CH₂CH₂ ¹⁸F.

In one embodiment, R₁₅ is —CH₂CH₂CH₂CH₂ ¹⁸F.

In one embodiment, R₁₅ is —CH₂CH₂CH₂CH₂CH₂ ¹⁸F.

In one embodiment, R₁₅ is —CH₂CH₂CH₂CH₂CH₂CH₂ ¹⁸F.

In one preferred embodiment, R₁₅ is —CH₂CH₂CH₂ ¹⁸F.

In one embodiment, R₁₅ is a ¹⁸F-labeled polyethylene glycol, e.g. 2K-,5K-, 10K-, 12K-, 15K-PEG.

In one embodiment, R₁₅ is —(CH₂CH₂O)_(m)CH₂CH₂ ¹⁸F, wherein m is 1-50,preferably m is 1-25, more preferably m is 1-10, and most preferably mis 1-4.

In one preferred embodiment, R₁₅ is —CH₂CH₂OCH₂CH₂ ¹⁸F.

Another aspect of the present invention is directed toward a compositionincluding a fluorine-18 labeled rhodamine derivative according toformula I or II and a pharmaceutically acceptable carrier.

As used herein, the term “acceptable pharmaceutical carrier” includesmaterial, composition or vehicle, such as a liquid or solid filler,diluent, excipient, solvent or encapsulating material, involved inmaintaining the agent in a deliverable form or in carrying ortransporting the active agent from one organ, or portion of the body, toanother organ, or portion of the body. Each carrier must be “acceptable”in the sense of being compatible with the other ingredients of theformulation and not injurious to the subject.

Some examples of materials which can serve as acceptable pharmaceuticalcarriers include, but are not limited to, (1) sugars, such as lactose,glucose, saccharin and sucrose; (2) starches, such as corn starch andpotato starch; (3) cellulose, and its derivatives, such as sodiumcarboxymethyl cellulose, ethyl cellulose and cellulose acetate; (4)powdered tragacanth; (5) malt; (6) gelatin; (7) talc; (8) excipients,such as dicalcium phosphate, cocoa butter and suppository waxes; (9)oils, such as peanut oil, cottonseed oil, safflower oil, sesame oil,olive oil, corn oil and soybean oil; (10) glycols, such as propleneglycol; (11) polyols, such as glycerine, sorbitol, mannitol andpolyethylene glycol; (12) esters, such as ethyl oleate and ethyllaurate; (13) agar; (14) buffering agents, such as magnesium hydroxideand aluminum hydroxide; (15) alginic acid; (16) pyrogen-free water; (17)isotonic saline; (18) Ringer's solution; (19) ethyl alcohol; (20)phosphate buffer solution; (21) acacia; (22) lubricants, such asmagnesium stearate and sodium lauryl sulfate; (23) preservatives, suchas methyl and propylparabens; (24) dyes; (25) wetting agents; (26)emulsifiers; (27) coloring agents; (28) release agents; (29) coatingagents; (30) flavoring agents; (31) perfuming agents; (32) sweeteningagents; (33) antioxidants, such as ascorbic acid, cysteinehydrochloride, sodium bisulfate, sodium metabisulfite, ascorbylpalmitate, butylated hydroxyanisole, citric acid, ethylenediaminetetraacetic acid (EDTA), sorbitol, tartaric acid, phosphoric acid, andthe like; and (24) other non-toxic compatible substances employed inpharmaceutical formulations.

Another aspect of the present invention is directed toward a method ofobtaining a positron emission image of a portion of a mammal includingadministering to a mammal a fluorine-18 labeled rhodamine derivativeaccording to formula I or II and acquiring a positron emission image ofa portion of a mammal. The mammal may be a human. The portion of themammal may be the myocardium.

A further aspect of the present invention is directed toward a method ofimaging myocardial perfusion including administering to a patient afluorine-18 labeled rhodamine derivative according to formula I or IIand scanning the patient using diagnostic imaging.

A further aspect of the present invention is directed toward use of afluorine-18 labeled rhodamine derivative according to formula I or IIfor the production of an imaging agent for carrying out myocardialperfusion imaging.

A still further aspect of the present invention is directed toward useof a fluorine-18 labeled rhodamine derivative according to formula I orII in the manufacture of an imaging agent for carrying outpositron-emission tomography.

In one aspect the invention provides a compound comprising an ¹⁸Flabeled rhodamine derivative according to formula I or II:

wherein R₁, R₂, R₃, R₄, and R₅ are each independently selected from thegroup consisting of hydrogen, substituted or unsubstituted alkyl,substituted or unsubstituted alkenyl, substituted or unsubstitutedalkynyl, substituted or unsubstituted heterocycloalkyl, substituted orunsubstituted alkoxy, substituted or unsubstituted carbonyl, acylamino,halogen, halogen radioisotope, substituted or unsubstituted aryl,substituted or unsubstituted heteroaryl, substituted or unsubstitutedamino, substituted or unsubstituted alkylamino, substituted orunsubstituted arylamino, isothiocyano and a compound of formula III

wherein R₁₀, R₁₁, R₁₂, R₁₃ and R₁₄ are each independently selected fromthe group consisting of hydrogen, substituted or unsubstituted alkyl,substituted or unsubstituted alkenyl, substituted or unsubstitutedalkynyl, substituted or unsubstituted heterocycloalkyl, substituted orunsubstituted alkoxy, substituted or unsubstituted carbonyl, acylamino,halogen, halogen radioisotope, substituted or unsubstituted aryl,substituted or unsubstituted heteroaryl, substituted or unsubstitutedamino, substituted or unsubstituted alkylamino, substituted orunsubstituted arylamino and isothiocyano;

wherein R₂ and R₃, taken together with the nitrogen atom to which theyare attached, may optionally form a substituted or unsubstitutedheterocyclic ring system;

R₂ and R₁₀, taken together with the atoms to which they are attached,may optionally form a 5- or 6-membered heterocyclic ring;

R₂ and R₁, taken together with the atoms to which they are attached, mayoptionally form a 5- or 6-membered heterocyclic ring; and

R₃ and R₄, taken together with the atoms to which they are attached, mayoptionally form a 5- or 6-membered heterocyclic ring or a substituted orunsubstituted heterocyclic ring system;

A₁ is carbon or nitrogen, if A₁ is nitrogen, then R₆ is absent;

R₆ is absent or selected from the group consisting of hydrogen,substituted or unsubstituted alkyl, substituted or unsubstitutedalkenyl, substituted or unsubstituted alkynyl, substituted orunsubstituted heterocycloalkyl, substituted or unsubstituted alkoxy,substituted or unsubstituted carbonyl, acylamino, halogen, halogenradioisotope, substituted or unsubstituted aryl, substituted orunsubstituted heteroaryl, substituted or unsubstituted amino,substituted or unsubstituted alkylamino, substituted or unsubstitutedarylamino, isothiocyano;

R₇, R₈ and R₉ are each independently selected from the group consistingof hydrogen, substituted or unsubstituted alkyl, substituted orunsubstituted alkenyl, substituted or unsubstituted alkynyl, substitutedor unsubstituted heterocycloalkyl, substituted or unsubstituted alkoxy,substituted or unsubstituted carbonyl, acylamino, halogen, halogenradioisotope, substituted or unsubstituted aryl, substituted orunsubstituted heteroaryl, substituted or unsubstituted amino,substituted or unsubstituted alkylamino, substituted or unsubstitutedarylamino, isothiocyano;

R₁₅ is independently selected from the group consisting of ¹⁸F-labeledsubstituted or unsubstituted alkyl, ¹⁸F-labeled substituted orunsubstituted alkenyl, ¹⁸F-labeled substituted or unsubstituted alkynyl,¹⁸F-labeled substituted or unsubstituted heterocycloalkyl, ¹⁸F-labeledsubstituted or unsubstituted alkoxy, ¹⁸F-labeled substituted orunsubstituted carbonyl, ¹⁸F-labeled acylamino, halogen radioisotope,¹⁸F-labeled substituted or unsubstituted aryl, ¹⁸F-labeled substitutedor unsubstituted heteroaryl, ¹⁸F-labeled substituted or unsubstitutedamino, ¹⁸F-labeled substituted or unsubstituted alkylamino, ¹⁸F-labeledsubstituted or unsubstituted arylamino, ¹⁸F-labeled isothiocyano, and—(CH₂CH₂O)_(m)CH₂CH₂ ¹⁸F, wherein m is 1-50;

R₁₆ is independently selected from the group consisting of hydrogen,substituted or unsubstituted alkyl, substituted or unsubstitutedalkenyl, substituted or unsubstituted alkynyl, substituted orunsubstituted heterocycloalkyl, substituted or unsubstituted alkoxy,substituted or unsubstituted carbonyl, acylamino, halogen, halogenradioisotope, substituted or unsubstituted aryl, substituted orunsubstituted heteroaryl, substituted or unsubstituted amino,substituted or unsubstituted alkylamino, substituted or unsubstitutedarylamino, isothiocyano; and

A- is an anion.

DEFINITIONS

The term “alkyl” as used herein refers to saturated straight-chain,branched-chain or cyclic hydrocarbon radicals. Examples of alkylradicals include, but are not limited to, methyl, ethyl, propyl,isopropyl, n-butyl, tert-butyl, neopentyl, n-hexyl, cyclohexyl, n-octyl,n-decyl, n-dodecyl and n-hexadecyl radicals.

The term “alkenyl” as used herein refers to unsaturated straight-chain,branched-chain or cyclic hydrocarbon radicals having at least onecarbon-carbon double bond. Examples of alkenyl radicals include, but arenot limited to, allyl, butenyl, hexenyl and cyclohexenyl radicals.

The term “alkynyl” as used herein refers to unsaturated hydrocarbonradicals having at least one carbon-carbon triple bond. Representativealkynyl groups include, but are not limited to, ethynyl, 1-propynyl,1-butyryl, isopentynyl, 1,3-hexadiynyl, n-hexynyl, 3-pentynyl,1-hexen-3-ynyl and the like.

The terms “halo” and “halogen”, as used herein, refer to an atomselected from fluorine, chlorine, bromine and iodine. The term “halogenradioisotope” refers to a radionuclide of an atom selected fromfluorine, chlorine, bromine and iodine.

The term “aryl,” as used herein, refers to a mono-, bicyclic, ortricyclic carbocyclic ring system having one, two or three aromaticrings including, but not limited to, phenyl, naphthyl, anthryl, azulyl,tetrahydronaphthyl, indanyl, indenyl and the like.

The term “heteroaryl,” as used herein, refers to a cyclic aromaticradical having from five to ten ring atoms of which one ring atom isselected from S, O and N; zero, one or two ring atoms are additionalheteroatoms independently selected from S, O and N; and the remainingring atoms are carbon, the radical being joined to the rest of themolecule via any of the ring atoms, such as, for example, pyridinyl,pyrazinyl, pyrimidinyl, pyrrolyl, pyrazolyl, imidazolyl, thiazolyl,oxazolyl, isooxazolyl, thiadiazolyl, oxadiazolyl, thiophenyl, furanyl,quinolinyl, isoquinolinyl, and the like.

The term “heterocycloalkyl,” as used herein, refers to a non-aromatic3-, 4-, 5-, 6- or 7-membered ring or a bi- or tri-cyclic groupcomprising fused six-membered rings having between one and threeheteroatoms independently selected from oxygen, sulfur and nitrogen,wherein (i) each 5-membered ring has 0 to 1 double bonds and each6-membered ring has 0 to 2 double bonds, (ii) the nitrogen and sulfurheteroatoms may optionally be oxidized, (iii) the nitrogen heteroatommay optionally be quaternized, and (iv) any of the above heterocyclicrings may be fused to a benzene ring. Representative heterocyclesinclude, but are not limited to, pyrrolidinyl, pyrazolinyl,pyrazolidinyl, imidazolinyl, imidazolidinyl, piperidinyl, piperazinyl,oxazolidinyl, isoxazolidinyl, morpholinyl, thiazolidinyl,isothiazolidinyl, and tetrahydrofuryl.

The term “carbonyl” as used herein refers to a carbonyl group, attachedto the parent molecular moiety through the carbon atom, this carbon atomalso bearing a hydrogen atom, or in the case of a “substituted carbonyl”a substituent as described in the definition of “substituted” below.

The term “acyl” as used herein refers to groups containing a carbonylmoiety. Examples of acyl radicals include, but are not limited to,formyl, acetyl, propionyl, benzoyl and naphthoyl.

The term “alkoxy”, as used herein, refers to a substituted orunsubstituted alkyl, alkenyl or heterocycloalkyl group, as previouslydefined, attached to the parent molecular moiety through an oxygen atom.Examples of alkoxy radicals include, but are not limited to, methoxy,ethoxy, propoxy, isopropoxy, n-butoxy, tert-butoxy, neopentoxy andn-hexoxy.

The term “aryloxy” as used herein refers to a substituted orunsubstituted aryl or heteroaryl group, as previously defined, attachedto the parent molecular moiety through an oxygen atom. Examples ofaryloxy include, but are not limited to, phenoxy, p-methylphenoxy,naphthoxy and the like.

The term “alkylamino”, as used herein, refers to a substituted orunsubstituted alkyl, alkenyl or heterocycloalkyl group, as previouslydefined, attached to the parent molecular moiety through a nitrogenatom. Examples of alkylamino radicals include, but are not limited to,methylamino, ethylamino, hexylamino and dodecylamino.

The term “arylamino”, as used herein, refers to a substituted orunsubstituted aryl or heteroaryl group, as previously defined, attachedto the parent molecular moiety through a nitrogen atom.

The term “substituted” as used herein in phrases such as “substitutedalkyl”, “substituted alkenyl”, “substituted aryl”, “substitutedheteroaryl”, “substituted heterocycloalkyl”, “substituted carbonyl”,“substituted alkoxy”, “substituted acyl”, “substituted amino”,“substituted aryloxy”, “substituted amido”, and the like, refers toindependent replacement of one or more of the hydrogen atoms on thesubstituted moiety with substituents independently selected from, butnot limited to, alkyl, alkenyl, heterocycloalkyl, alkoxy, aryloxy,hydroxy, amino, amido, alkylamino, arylamino, cyano, halo, mercapto,nitro, carbonyl, acyl, aryl and heteroaryl groups.

The term “substituted” as used herein in phrases such as “substitutednitrogen”, “substituted oxygen” and “substituted sulfur” refers tonitrogen, oxygen or sulfur substituted with alkyl, aryl, or heteroarylgroups. Examples include, but are not limited to, alkyl and aryl etherssuch as methoxy, ethoxy or phenoxy; alkyl or aryl thioethers such asthiomethoxy, thioethoxy and thiophenyl; alkyl or aryl amines such asdimethyl amino, diethylamino, diphenylamino, phenylamino, andN-methyl-N-phenylamino.

The compounds according to the invention may be prepared by syntheticprocesses which are known to those skilled in the art, particularly inview of the state of the art and the specific preparatory examplesprovided below herein.

Phenyl xanthene dyes can be prepared as described in U.S. Patent Pub.No. US 2004/0242902. Rhodamine dyes are described in U.S. Patent Pub.No. US 2006/0293523, U.S. Patent Pub. No. US 2007/0048640, U.S. Pat. No.4,647,675, U.S. Pat. No. 4,895,961, U.S. Pat. No. 4,602,263, U.S. Pat.No. 4,826,976, and U.S. Pat. No. 516,584.

Generally, symmetrical rhodamine dyes can be prepared in one step from3′,6′-dichlorofluorans by reacting two equivalents of an aromatic oraliphatic amine as described in U.S. Pat. No. 4,602,263, GB2311075 andDE81056. The unsymmetrical rhodamine dyes are then prepared by theselective monoalkylation of symmetrical rhodamines using sodium hydridein dimethyl sulfoxide as described in U.S. Pat. Nos. 4,602,263 and4,826,976.

Alternatively these novel unsymmetrical rhodamines can be prepared byuse of an alternate synthetic pathway in which one equivalent of anN-alkylaniline is reacted selectively with the 3′,6′-dichlorofluoranusing aluminum chloride as a catalyst to produce3′-chloro-6′-N-alkyl-N-arylfluorans. These products are isolated andpurified prior to reacting with a second equivalent of an aromatic oraliphatic amine. Zinc chloride is used as the catalyst for the secondaddition. DE139727 describes the selective addition of anilines to3′,6′-dichlorofluorans to produce 3′-chloro-6′-arylaminofluorans using amixture of zinc chloride and zinc oxide at 160° C.

Unsymmetrical rhodamines can also be made from 2-benzoyl benzoic acidderivatives by condensation with 3-arylamino phenols or 3-alkylaminophenols as described in Chemistry and Applications of Leuco Dyes, pp.180-191 R. Muthyala, Ed., Plenum Press, New York and London, 1997 andalso U.S. Pat. Nos. 4,390,616 and 4,436,920.

Unless otherwise defined herein, scientific and technical terms used inconnection with the present application shall have the meanings that arecommonly understood by those of ordinary skill in the art. Further,unless otherwise required by context, singular terms shall includepluralities and plural terms shall include the singular.

It should be understood that this invention is not limited to theparticular methodology, protocols, and reagents, etc., described hereinand as such may vary. The terminology used herein is for the purpose ofdescribing particular embodiments only, and is not intended to limit thescope of the present invention, which is defined solely by the claims.

Other than in the operating examples, or where otherwise indicated, allnumbers expressing quantities of ingredients or reaction conditions usedherein should be understood as modified in all instances by the term“about.” The term “about” when used in connection with percentages maymean±1%.

All patents and other publications identified are expressly incorporatedherein by reference for the purpose of describing and disclosing, forexample, the methodologies described in such publications that might beused in connection with the present invention. These publications areprovided solely for their disclosure prior to the filing date of thepresent application. Nothing in this regard should be construed as anadmission that the inventors are not entitled to antedate suchdisclosure by virtue of prior invention or for any other reason. Allstatements as to the date or representation as to the contents of thesedocuments is based on the information available to the applicants anddoes not constitute any admission as to the correctness of the dates orcontents of these documents.

EXAMPLES Example 1 Synthesis of 2-¹⁸F-fluoroethyl Ester of Rhodamine BPreparation of precursor-2-¹⁸F-fluorethyltosylate

Ethylenebistosylate is reacted with dry [¹⁸F]fluoride, Kryptofix 2.2.2(K2.2.2) and potassium carbonate in anhydrous acetonitrile at 100° C.for 10 min. in a Pierce “V-vial” to produce the 2-¹⁸F-fluorethyltosylatein 80-85% yield. The product may be purified by solid-phase extractionor chromatographically (e.g., semi-preparative HPLC). See FIG. 1.

Preparation of 2-¹⁸F-fluoroethyl ester of rhodamine B

2-¹⁸F-fluorethyltosylate is added to a solution of rhodamine B lactoneand diisopropylethylamine (DIPEA) in anhydrous acetonitrile and heatedat 160° C. for 30 min. to produce the ¹⁸F-labeled fluorethyl ester in˜35% yield. The product may be purified by solid-phase extraction orchromatographically (e.g., semi-preparative HPLC). See FIG. 2. “One-Pot”Synthesis of 2-¹⁸F-fluoroethyl ester of rhodamine B

This reaction proceeds as outlined above but without isolation of the2-¹⁸F-fluorethyltosylate precursor. Ethylenebistosylate is reacted withdry [¹⁸F]fluoride, Kryptofix 2.2.2 (K2.2.2) and potassium carbonate inanhydrous acetonitrile at 100° C. for 10 min. in a Pierce “V-vial” toproduce the 2-¹⁸F-fluorethyltosylate (80-85% yield). Rhodamine B lactoneand DIPEA are added directly to the crude 2-¹⁸F-fluorethyltosylatesolution and heated for an additional 30 min. at 160° C. The finalproduct, the 2-¹⁸F-fluoroethylester of rhodamine B, is obtained inapproximately 35% yield after purification by semi-preparative HPLC. Thetotal reaction time is approximately 45 min. See FIG. 3. See Lu et al.J. Label. Compd. Radiopharm. 2004, 47: 289-97.

Example 2 Synthesis of 3-¹⁸F-fluoropropyl Ester of Rhodamine B

The 3-¹⁸F-fluoropropyl ester of rhodamine B is synthesized using theprotocols outlined in Example 1 and starting with1,3-bis-tosylate-propane. The final product, 3-¹⁸F-fluoropropylester ofrhodamine B, was obtained in approximately 28% yield after purificationby semi-preparative HPLC.

Example 3 Synthesis of 5-¹⁸F-fluoro-3-oxa-pentyl Ester of Rhodamine B

The ¹⁸F-labeled diethylene glycol ester of Rhodamine B is prepared usingthe protocols outlined in Example 1 and starting with3-oxapentane-1,5-bistosylate. FluorodiethylenegycolTos(5-¹⁸F-fluoro-3-oxa-pentyl-tosylate) was prepared fromdiethyleneglycol-ditosylate (123 mg, 0.39 mmol), potassium fluoride (25mg, 0.43 mmol) and Kryptofix (200 mg, 0.53 mmol) in 5 mL of acetonitrileheated at 75° C. for 2 h. as described by Studenov, et al. NuclearMedicine and Biology 28 (2001) 683-693. The product was obtained as oilin 60% yield. The FluorodiethylenegycolTos was reacted with rhodamine Blactone as outlined in Example 1. The final product,5-¹⁸F-fluoro-3-oxa-pentyl ester of rhodamine B, was obtained inapproximately 27% yield after purification by semi-preparative HPLC.

Example 4 Synthesis of 2-F-fluoroethyl Ester of Rhodamine 110 as coldreference compound for esters

Rhodamine 110 is heated in 2-fluoroethanol at 120° C. for 24 h andpurified on C18 reversed phase silica gel to deliver the Fluoroethylester in 50% yield. See FIG. 4.

Example 5 Synthesis of 3-fluoropropyl Ester of Rhodamine B (FERhB) ascold reference compound for esters

The nonradioactive 3-fluoropropyl ester of rhodamine B was prepared bytransesterification of rhodamine B lactone with 3-fluoropropylp-toluenesulfonate. 88.4 mg of rhodamine B lactone (0.2 mmol) weredissolved in 4 mL acetonitrile to which 55.5 mg 3-fluoropropylp-toluenesulfonate (0.23 mmol, previously dissolved in 1 mLacetonitrile) and 0.178 mL (1 mmol) diisopropylethylamine were added.The solution was refluxed and the reaction was monitored by TLC. After24 h, 50% of the rhodamine B lactone starting material had beenconverted to the 3-fluoropropyl ester, at which time the heating wasdiscontinued, the reaction mixture was allowed to cool to roomtemperature, and then evaporated to dryness to give approx. 50 mg ofcrude product as a dark red oil. 10 mg of the crude product was purifiedby semi-preparative HPLC to provide 5 mg (50%) of purified FPRhB as apurple solid

Example 6 Synthesis of 5-fluoro-3-oxa-pentyl Ester of Rhodamine B(FERhB) as cold reference compound for esters

The nonradioactive 5′-fluorodiethylenegycol ester of rhodamine B wasprepared by transesterification of rhodamine B ketone with5-fluoroethyleneglycol p-toluenesulfonate. 25 mg of 1 (0.056 mmol) weredissolved in 3 mL acetonitrile to which 17.5 mg 5-fluorodiethyleneglycolp-toluenesulfonate (0.067 mmol, previously dissolved in 2 mLacetonitrile) and 0.05 mL (0.294 mmol) diisopropylethylamine were added.The solution was refluxed and the reaction was monitored by HPLC. After2 h, 60% of the rhodamine B lactone starting material had been convertedto the 5-fluorodiethylenegycol ester, at which time the heating wasdiscontinued, the reaction mixture was allowed to cool to roomtemperature, and then evaporated to dryness to give approx. 19 mg ofcrude product as dark red oil. 10 mg of the crude product was purifiedby semi-preparative HPLC to provide 7 mg (70%) of purified FEGRhB as apurple solid.

Example 7 Preparation of precursor-2-¹⁸F-fluorethylamine for amidesynthesis

Fluoroethylamine was made according to literature starting either from(2-methoxy-ethyl)-carbamic acid tert-butyl ester or2-(2-methoxy-ethyl)-isoindole-1,3-dione, which is reacted with dry[¹⁸F]fluoride, Kryptofix 2.2.2 (K2.2.2) and potassium carbonate inanhydrous acetonitrile at 100° C. for 10 min. in a Pierce “V-vial” toproduce the 2-¹⁸F-fluorethylamine after cleavage of the protecting groupin 15 respectively 60% radiochemical yield. The product may be purifiedby solid-phase extraction or HPLC. See FIG. 5.

Example 8 Preparation of 2-¹⁸F-fluoroethyl amide of rhodamine 110

2-¹⁸F-fluorethylamine is added to a solution of rhodamine 110 inChloroform and dicyclohexyl carbodiimide is added also in Chloroform andstirred at 40° C. for 20 min. to produce the ¹⁸F-labeled fluoroethylamide in ˜25% yield. The product may be purified by solid-phaseextraction or semipreparative. HPLC. See FIG. 5.

Example 9 Direct labeling of 2-¹⁸F-fluoroethyl amide of rhodamine 110

This reaction proceeds from a direct labeling precursor, e.gmethanesulfonic acid benzoylamino-ethyl ester is reacted with dry[¹⁸F]fluoride, Kryptofix 2.2.2 (K2.2.2) and potassium carbonate inanhydrous acetonitrile at 100° C. for 10 min. in a Pierce “V-vial” toproduce the 2-¹⁸F-fluorethylamide (20-25% yield). See FIG. 6.

Although preferred embodiments have been depicted and described indetail herein, it will be apparent to those skilled in the relevant artthat various modifications, additions, substitutions, and the like canbe made without departing from the spirit of the invention and these aretherefore considered to be within the scope of the invention as definedin the claims which follow.

All references disclosed herein are incorporated by reference in theirentirety.

REFERENCES

-   1. Vora, M. et al., Nucl. Med. Biol. 19(3):405-410, 1992.-   2. Studenov, A. et al., Nucl. Med. Biol. 28:683-693, 2001.-   3. Madar, I. et al., J. Nucl. Med. 48(6):1021-1030, 2007.-   4. Madar, I. et al., J. Nucl. Med. 47(8):1359-1366, 2006.-   5. Ravert, H. et al., J Label Compd Radiopharm 47:469-476, 2004.-   6. VanBrocklin, H. et al., Nucl. Med. Biol. 34:109-116, 2007.-   7. Madar, I. et al., “¹⁸F-Fluorobenzyltriphenyl phosphonium PET    detects area-specific apoptosis in the aging myocardium” Society of    Nuclear Medicine, Annual Meeting Abstracts Abstract No. 562, 2007.-   8. Shoup, T. M. et al., “Evaluation of    (4-[¹⁸F]Fluorophenyl)Triphenylphosphonium Ion as a Potential    Myocardial Blood Flow Agent for PET” Abstract Book Supplement to J.    Nucl. Med. Oral Presentation Abstract No. 178.-   9. Lu et al. J. Label. Compd. Radiopharm. 2004, 47: 289-97.-   10. Gilissen, C., et al., J. Label. Compd. Radiopharm., 41(6):    491-502 (1998).-   11. Jelinski, M., et al., J. Label. Compd. Radiopharm., 45(3):    217-229 (2002).-   12. Lehel, Sz. et al., J. Label. Compd. Radiopharm., 43(8): 807-815    (2000).-   13. Zhang, M-R., et al., J. Label. Compd. Radiopharm., 46: 587-598    (2003).

What is claimed is:
 1. A compound comprising an ¹⁸F labeled rhodaminederivative according to formula I:

wherein R₁, R₃, and R₅ are hydrogen; R₂ and R₄ are alkyl; A₁ is carbonor nitrogen, if A₁ is nitrogen, then R₆ is absent; R₆ is hydrogen; R₇,R₈ and R₉ are hydrogen; R₁₅ is —(CH₂CH₂O)_(m)CH₂CH₂ ¹⁸F, wherein m is1-50; and A- is an anion.
 2. The compound of claim 1, wherein R₁, R₃,R₅, R₆, R₇, R₈, and R₉ are hydrogen; and A₁ is carbon.
 3. The compoundof claim 1, wherein R₂ is ethyl.
 4. The compound of claim 1, wherein R₄is methyl.
 5. The compound of claim 1, wherein R₁₅ is—(CH₂CH₂O)_(m)CH₂CH₂ ¹⁸F, wherein m is 1-4.
 6. The compound of claim 5,wherein R₁₅ is —CH₂CH₂OCH₂CH₂ ¹⁸F.
 7. The compound of claim 1, whereinR₁, R₃, R₅, R₆, R₇, R₈, and R₉ are hydrogen; R₂ is ethyl; R₄ is methyl;R₁₅ is —CH₂CH₂OCH₂CH₂ ¹⁸F; and A₁ is carbon.
 8. The compound of claim 1,wherein the compound is a myocardial positron imagining agent.
 9. Apharmaceutical composition comprising a compound of claim 1 and apharmaceutically acceptable carrier.
 10. A method of obtaining apositron emission image of a portion of a mammal, comprising the stepsof: administering to a mammal a compound of claim 1; and acquiring apositron emission image of a portion of a mammal, wherein said portionof a mammal is the myocardium.
 11. The method of claim 10 wherein themammal is a human.
 12. A method of imaging myocardial perfusioncomprising: administering to a patient a compound of claim 1; andscanning the patient using diagnostic imaging.